It should be ok, just get it checked over. make sure the alternator is giving an output.
Starter motor shouldn't be an issue, as it seems to start first time alright after a boost.
When was the battery last replaced? (Might be a date sticker on it somewhere)
Most fog lights use the same amount of power as mainbeam headlights being switch on - both can drain the battery rapidly (for example, mine has a near new 55AH battery in and it only takes about 2 minutes with the headlights on for the battery to drain)
It will obviously drain a lot faster if the battery is not fully charged. Mostly drains quicker after many short journeys as battery isn't given enough time to become charged up by the alternator.
So, just give the car a good run or charge the battery.
At the very most, a new battery may be needed (£50) and perhaps an alternator, but if you've never had a problem with the battery before, most likely neither lol
Hope this helps